438 PALEONTOLOGY OF ILLINOIS. 



STENOPORA MONTIFERA Ulrich. 



PI. LXXIV, fig. 4-4b. 



Zoarium consisting of thin laminae, which sometimes appear 

 to have been part of large hollow branches. Surface with large 

 and very prominent monticules. Zooecia eight to ten in three 

 mm.; generally with very thin walls and angular apertures. Re- 

 maining external features like those of S. americana, of which 

 it may be only a good variety. 



The internal structure of these specimens differs slightly from 

 that of typical S. americana, the periodic thickening of the 

 walls being more irregular, and the divisional line between the 

 zooecia marked by a closely arranged series of minute dark 

 spots, which are also to be detected in vertical sections. 



Position and locality: Keokuk group, Otter creek, Jersey Co., 

 111.; Bentonsport, Iowa, and other localities. 



STENOPOBA EMACIATA Ulrich. 



PL LXXIV. Fig. 2-2a. 



Zoarium laminar, attaining a considerable width; thickness 

 one mm. or more; under surface provided with a thin wrinkled 

 epitheca. Surface marked with groups of larger cells, which are 

 elevated into low broad monticules, about four mm. apart, 

 measuring from center to center. Apertures polygonal, varying 

 in width from 0.3 mm, in the intermacular spaces, to 0.5 in the 

 clusters, about eight or nine in three mm. Walls very thin, 

 spinose at the angles. Zooecial tubes bending toward the sur- 

 face very soon after their origin. Walls very thin throughout, 

 but appreciably thickened at intervals, about seven times in two 

 mm. Mesopores wanting. Perforated diaphragms very thin, a 

 tube diameter or so apart. Acanthopores small, excepting in 

 the clusters of large cells, commonly at the angles, protruding 

 more or less into the zocecial chambers. 



The very thin walls and more numerous diaphragms distin- 

 guish this species from S. montifera. S. tuberculata Prout, 

 differs somewhat in growth, and has the walls more decidedly 

 thickened and at shorter intervals. The diaphragms are also 

 more numerous. 



Position and locality: Keokuk group; Warsaw, 111., and 

 Keokuk, Iowa. 



